Some progress, I tried this:
Which generated this response:
Therefore quite likely this this is not possible with the Download directory using SAF. I will attempt to streamline the copy, copy, delete, delete method that works.
Yes, copying does not seem to be an issue. Filetools is not required for that. I have the file component on board. But thanks, i have not tried that way yet.
Yes, it's only for showing the source file path.
After that you can remove the file from /Download, so it's the same like moving it then.
Yes, that is much better, copying directly to the sub-directory, then deleting the file in Download.
The aim is to then have a directory that replicates Download, in order to be able to use SAF to provide a list of files in that directory, just as one can with all the other shared directories. Just a pain to have to do the copying one by one.
And unfortunately, it does not seem possible to create a sub-directory in Download using SAF, unless you manually do it when opening the document tree to Download.
What's the problem with doing it using the File component or FileTools?
No problem, exploring SAF possibilities 
...are only relevant on Android 11+. Whenever possible, avoid this.
As I said before, there are no problems copying/moving media files to a subfolder of /Download (or wherever). The problem only arises with non-media files (not created by the app), and those would have to be individually selected and copied/moved to the subfolder. There is no other way—without MANAGE_EXTERNAL_STORAGE.
Unless, as we have both demonstrated, you use SAF...
Isn't that exactly what I'm talking about?
You seem to talk about everything except SAF. As I indicated at the start, my aim is to see what I can do with just SAF, instead of having to mess about with permissions. Also, given the enforcement of the Photo and Video Permissions Policy, the application of the "MEDIA" permissions in an app will now require a declaration of intent for the Play Store.
No, what else should I talk about here if not SAF??
SAF working fine with Android 6 device here, just wanted to qualify that. I understand what you are saying regarding relevance.
I didn't bother to read any background information on SAF, because I am an idiot.
Idiot comes from the Greek (ἰδιώτης) and actually means "private person", not "expert." That's all. But you're certainly an expert when it comes to App Inventor. 
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13 posts were split to a new topic: When I pick an image using picker, I get READ_MEDIA_IMAGES has been denied
Dear @Anke, nice to read that. Me too, I've studied ancient greek and latin more than 50 years ago at the classic lyceum (as we call that type of school here in Italy), before discovering the charm of physics... 
German language has many similarities with ancient greek and latin: so I loved to study it (German) but the problem has been the short time remaining to do that after a "long" working day and an eveving to dedicate to the kids....maybe next life.... 
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